Sun Room Addition Lateral Analysis/Design

[wayniac3]

I have be asked to design a one story 20' x 12' sun room out of wood. It will have a gable roof with a mean roof height of 15'. The sun room is to be placed the back of a two story brick veneer house. It will be located in a 100 mph wind zone. The client wishes to have the sunroom built on a c.m.u./brick perimeter foundation wall in order to get the sun room floor to match the existing house floor level. I do not wish to attach the sun room to the brick veneer on the house. Therefore, I am at a bit of a loss as to how to provide adequate lateral bracing and foundation anchorage for the sun room as the client wishes have the walls for the most part consist of windows with 6x6 posts between. Could I get some input on how to approach this one?

 

[hokie66]

There are really only two ways without shear walls: rigid frames or braced bays. With wood, rigid frames probably won't work, especially with only 6x6 posts. That leaves bracing in some of the bays. Diagonal braces, either T-C diagonals, or tension x-braces, may be a solution, provided your client doesn't mind the look. Otherwise, you may be looking for a different material than wood.

 

[JAE]

Another way is to utilize a special roof diaphragm to cantilever off the main house. This will require a flat ceiling in the sun room, special connections to the main roof, possible special framing within the main roof/ceilng to distribute the shear and moment from the sun room diaphragm-cantilever, and a check of the diaphragm deflections to ensure adequate rigidity.

Also, since you have very little "wall" lengths, you should check the wind uplift on all those posts between windows and provided engineered tie-downs at the roof and foundation level.

And one further thing...chasing down the load path....be sure to check that the post holddown uplift forces are fully developed down to the footings. With msonry block foundation walls, you could possibly anchor bolt into the top course and not develop the vertical rebar in the wall to hold-down the top course.

 

[MiketheEngineer]

I have used JAE's solution for these types of additions. Workr just fine - actaully builders have been kind of doing it that way for years. Now we must prove they were correct and design the connections.

 

[wayniac3]

Thanks for the responses. I find them helpful. However, I will not be able to tie into the roof of the existing house. It is a two story house and I am designing only a one story sunroom addition. Is it possible to remove portions of brick to tie into the existing house structure to tie the sun room to the existing structure (say at the top and bottom wall plates). Or does this addition need to be built as a free standing structure butted up to the existing brick?

I think I may be able to talk the client into allowing me some wall space in the corners, therefore, I may be able to use the APA Portal Frame construction. Any thoughts would be appreciated.

 

[ishvaaag]

May be you can fix some colums to a stiffer roof, then tie the columns to the foundations, and then (if permissible) the roof to the main structure of the house, or add some complementary structure to make it work.

 

[KBVT]

Can't you tie your sunroom roof diaphragm back into the floor diaphragm of the main house? With the description you have provided, this can not be designed as a free-standing structure as you do not have adequate room for frames on you sunroom walls.

 

[wayniac3]

Thanks KBVT. That may be possible, but I am unsure of how to tie into the existing structure framing - I would need to penetrate the existing brick veneer. I don't know how to do this adequately to carry the imposed loads and loading the brick veneer and avoiding water penetration issues.

 

[JAE]

KBVT is on the right track.

You would need to punch holes into the brick at the additions "chord" locations (top of the new walls at the juncture of the new walls to the existing walls). Then some means of tying the new roof chords back into the floor framing (hopefully the floor joists are perpendicular to the existing exterior walls). This may require some partial demo of existing interior ceilings, etc. to get attachment to the floor diaphragm.

 

[msquared48]

You could also go to a pole footing scenario here at all the walls, to include the juncture with the house. The 6X6 could be steel tubing if necessary, either embedded into the foundation or bolted to it to gain fixity.

I have done this in the past coupled with short 2 to 4 foot high plywood shear exterior walls to decrease the pole bending length.

Mike McCann
MMC Engineering

 

[hokie66]

Personally, I would avoid attaching to the house. Too fiddly. Like Mike, I would look at a steel solution, with the steel posts both embedded and connected rigidly to steel header beams. I think I could convince my clients that this is the right solution, but I don't know your client.

 

[Stillerz]

This might be the most over-thought post I have seen here for a while.
You're making a sunroom addtion into nuclear power plant design.
Meet with the possible builder. Any builder with half an ass will be able to provide plenty of insight as to how you can actually build the room.
This type of addition is nothing new or special. You can't do ALL your engineering on paper.

 

[msquared48]

One learns by discussion. Therefore, discussion is good.

Mike McCann
MMC Engineering

 

[Stillerz]

true-
Dont know why I shot off like that.
Sorry...it was pathetic on my part.

 

[Stillerz]

It is probably because prior to being an educated engineer, I was a builder...and a builder of many additions like this one.
I know one thing, building an addition like this that is an order of magnitude more robust than the house is neither prudent nor logical...unless you are trying to hold the existing house in place.

 

[hokie66]

Stillerz,

In no way are any of us giving advice to build the sunroom more robust than the house. Building an enclosure 15' high with nothing but glass for walls is entirely different from building a two storey brick veneer house with lots of intended and unintended lateral stiffness.

 

[Stillerz]

All,

All apologies...not sure what my problem is today.
I am not even sure I read the original post thoroughly.
Please accept my apologies.

Regrets

 

[hokie66]

Stillerz,

Apology not required, but accepted. We all have our days...

 

[JAE]

Stillerz - keep poking your opinions in here, though. Lots of "thinking out loud" is good.

 

[Stillerz]

JAE- Is that a nice thick layer of sarcasm I detect?
If so, I deserve it.

I have done a few home additions similar to this, maybe not to this scale, but I think so.

I have dealt with is as follows:

Where the second floor diaphram is, (or in real world terms, the floor framing, floor joists and rim or box joists) located I would strip some of the brick away.
I would install pieces of LVL that I would call "frieze blocks" for lack of a better term. I would solidly fasten these 4" blocks to he floor framing with through-bolts and adhesive and would also put extra blocking between the floor joists in the existing house to tie this assembly further. I would then do the same in a few spots in the wall above the floor diaphram in locations where the truss will be.
The first truss to go against the existing house can then be attached to these "frieze blocks" as can the bottom chord bracing, nicely tying the addition to the existing house without relying on a brikc veneer.

This way, the overwhelming majority of the brick can be left in place and the parts that are disturbed hidden nicely.